1. Field of Invention
The present disclosure of invention relates to a signal processing device for a liquid crystal display and to a liquid crystal display having the same. More particularly, the present disclosure relates to a signal processing device having improved response speed.
2. Description of Related Technology
In general, a liquid crystal display (LCD) displays images using liquid crystals as optical shutters. However, since the liquid crystal display is a shutter-state holding-type display device, when moving images are to be displayed a blurring phenomenon can occur in which sharpness images of moving objects becomes low or the moving objects appear blurred or not transitioning smoothly from one location to a next.
In order to compensate for the slow response speed of the liquid crystals, a dynamic capacitance compensation (DCC) scheme has been developed.
FIGS. 1 and 2 are magnitude versus time waveform diagrams showing a conventional dynamic capacitance compensation scheme.
Referring to FIG. 1, image data of a previous frame, N−1 corresponds to a first to-be-attained or target voltage V1. Image data of a present frame, N corresponds to a second target voltage V2 higher than the first target voltage V1. In case that a voltage difference between the first and second target voltages V1 and V2 is larger than a predetermined reference value, although the second target voltage V2 is to be ultimately applied to the liquid crystals to achieve a corresponding target brightness L, that desired level L will not be immediately achieved by the liquid crystal display in frame N if just V2 is applied due to the slow response speed of the liquid crystals (represented by dashed option “A”). FIG. 1 shows an example where the target brightness level L will be achieved by the liquid crystal display only after about two frames if just V2 is applied (per dashed option “A”). The DCC scheme temporarily over-drives beyond the second target voltage V2, by using a slowness compensating voltage Vc that is higher than the second target voltage V2. Accordingly, when the over-driven compensation voltage Vc is applied to the liquid crystals during the present frame N, so that a crystal response time is shortened, thereby achieving the desired target brightness level L within one frame (the rise curve “B” shown in frame N).
However, as shown in FIG. 2, when the over-driven compensation voltage Vc is applied to the liquid crystals in a present frame, N while the brightness of the previous frame N−1 had not yet reached an earlier, first target brightness level, L1 corresponding to an earlier first target voltage (far below V2 and Vc), errors in crystal state accumulate and an excessive next brightness level, L3 is produced which is larger than the desired second target brightness level, L2. That is, although the DCC scheme is performed normally, in some cases an inordinate compensation voltage Vc is applied to the liquid crystals in the present frame N. As a result, an excessive brightness may be visually recognized (perceived) during the following present and next frames, N and N+1.